There’s no doubt that paddling a surfboard out to the breakers is a good source of upper body exercise. What a lot of non-surfers might not realize, however, is that balancing on a constantly-shifting board is also a great workout for the core muscle groups. Surfer and entrepreneur Mike Hartwick certainly realized it, which is why he created the RipSurfer X stationary surfboard trainer – while it’s far from being the world’s only balance trainer, it’s claimed to be unique in offering all the fitness benefits of real surfing.